Capacity control for reciprocating compressors



Dec. 15, 1959 L. HANSON ET AL 2,917,225

CAPACITY CONTROL FOR RECIPROCATING COMPRESSORS Filed Sept. 6, 1952 INVENTORS f1 5-1 1435 mwvso/v mam M- 597515 BY Q44 States Pat CAPACITY CONTROL FOR RECIPROCATING COMPRESSORS Application September 6, 1952, Serial No. 308,254

13 Claims. (Cl. 230-2) In the co-pending application of Carlyle M. Ashley, Serial No. 692,326, filed August 22, 1946 now Patent No. 2,626,099, issued January 20, 1953, entitled Capacity Control for Reciprocating Compressors, there is disclosed a system of capacity control for reciprocating compressors which includes oil pressure actuated elements for hold-t ing compressor valves in inoperative position, an oil pressure actuated member for permittingor discontinuing the passage of oil to the elements and a valve responsive to load conditions for varying the oil pressure imposed on the oil pressure actuated member to permit or to discontinue the supply of oil to the elements in sequence in accordance with load conditions.

The present invention is concerned with an improvement in this system of capacity control and is designed to prevent rapid recycling during operation of the come 7 2,917,225 Patented Dec. 15, 1959 which. serves as an oil sump 8, and operating mechanism including the usual crank shaft 9, pistons 10, connecting rods 11, and other structural elements, normally employed in compressing gas, all of which form no essential part of the invention, but which it will be understood are present to form an operable compressor.

Suitable unloading mechanism designated generally at 12 is provided to hold the suction valve 13 of a cylinder in an operable position. Mechanism 12 may be actuated by means of a power element 14 actuated by oil pressure. Any desired number of cylinders of the compressor may be'provided with unloading mechanism.

Apump 15 provides lubrication of moving parts of the compressor. A control valve 16 is connected to pump 15 by a line 17. A relief valve 18 is placed in line 17 to maintain a constant oil pressure to the moving pans of the compressor and to valve 16. Valve 16 is connected to the various power elements 14 by means of lines 19. Valve 16 serves to permit or to discontinue the supply of oil to each power element 14 in sequence, that is, one after the other as hereinafter described. A capacity control valve 20 is connected to valve 16 by means pressor by retarding response of the capacity control valve to changes in load imposed upon this system.

The chief object of the present invention is to provide a system of capacity control for reciprocating compressors which permits the capacity of a compressor to be adjusted in response to load conditions, so designed as to prevent rapid recycling during operation of the compressor.

An object of the invention is to provide a system of capacity control for a reciprocating compressor in which liquid pressure substantially equivalent to suction pres sure is employed to actuate the control element and means are provided to retard the response of the control element to changes in load imposed upon this system.

A further object is to provide a system of capacity control. for a reciprocating compressor having embodied therein a time delay in the responsive element thereby substantially eliminating rapid recycling during operation of the compressor. Other objects of the invention will be readily perceived from the following description.

This invention relates to a system of capacity control for reciprocating compressors which comprises oil pressure actuated elements for holding compressor valves in inoperative position, oil pressure actuated means for permitting or discontinuing the passage of oil to the elements, means responsive to load conditions for varying the oil pressure imposed on the pressure actuated means to permit or to discontinue the supply of oil to said ele-' ments in sequence to said elements in accordance with load conditions, and a control for retarding the response of said means to change in load conditions.

The attached drawings illustrate a preferred embodiment of the invention in which: s

Figure 1 is a diagrammatic view illustrating a compressor including the capacity control of the present invention;

Figure 2 is a diagrammatic view illustrating the capacity control of the present invention.

Referring to the attached drawings, there is shown in Figure 1 a compressor 2 having a plurality of cylinders 3, 4, 5 and 6. The compressor may be of any conventional design and includes a crank case 7, the bottom of of line 21 and serves to regulate or adjust valve 16 as hereinafter described. Valve 20 is connected to the sump 8 through line 22, surge chamber 23, capillary tube 24, and oil line 25. Such elements form retarding mechanism to delay response of control valve 20 as hereinafter described. Oil may be drained-from valve 21) to sump 8 through line 26.

Preferably, the capacity control is disposed in the pump end cover 27 of compressor 2rand oil is supplied thereto by pump 15.

The unloading mechanism 12 consists of lifter sleeve 31, lifter pin 32, loading springs 33, and a retaining ring 34. Suction gas from the manifold (not shown) enters suction valve port 35 and passes through such port into the interior of the compressor cylinder when valve 13 is moved away from port 35. When pins 32 are in the position illustrated in Figure 2, the suction valve 13 closes at the end of each suction stroke under the urging of springs (not shown). After compression of the gas in this cylinder, the gas is discharged through discharge valves (not shown) into the cylinder head space. Pins 32 remain retracted while full oil pressure is applied to power element 14 and are moved upward to hold valve 13 in inoperative position when oil pressure on element 14 is discontinued. Power element 14 consists of a casing 36 having a base 37 and a top cover 38. Piston 39 is placed in casing 36 and is connected by a rod 40 to a forked lever 41, operating on a fulcrum 4. placed at one end of cover 38. Lever 41 terminates in portions 43 adapted to engage the lifter sleeve 31 surrounding the cylinder. A piston spring 44 applies predetermined pressure to piston 39. In the absence of oil pressure supplied to element 14, piston 39 rests against the bottom cover 37. A vent45 is provided in power element 14 to permit oil which seeps past piston 39 to return to the crank case 7 of compressor 2. Preferably, the power elements 14 are located in the suction manifold of the compressor adjacent the cylinder to be unloaded.

When oil pressure is applied to element 14, piston 39 moves upward permitting lever 41 to pivot about fulcrum 42 thus permitting sleeve 31 to be urged downward by springs 33 until such movement is halted by contact of sleeve 31 against ring 34. Downward movement of sleeve 31 carries pins 32 therewith thus permitting suction valve 13 to be disposed in operative position. When pressure is removed from power element 14 as by, for example, discontinuing the passageof oil thereto, piston 39 is forced downward by spring 44, pivoting lever 41 about fulcrum 42 and urging sleeve 31 in an upward direction to raise pins 32 thus holding valve 13 away 3 from port 35 with the suction valve placed in an open position. No compression of gas takes place in the cylinder and the capacity of cylinder is zero.

Valve 16 is an oil pressure actuated, multiple port, snap action piston valve. Oil pressure is supplied to acliamber 50 of valve 16 through line 17. Piston 51 is placed in chamber 50. Piston 51 is provided with grooves 52. A spring 53 is held in chamber 50 by cap 54 to provide a predetermined pressure to urge piston 51 longitudinally of chamber 50. The end of piston 51 serves in efiect as a partition separating or dividing chamber 50 from a second chamber 56. End opening 57 in end 55 connects chambers 50 and 56. Chamber 56 is connected to capacity control valve 20 by line 21.

A plurality of outlets 58 are provided in chamber 50 and are connected to lines 19 leading 'to the various power elements 14. An opening 59 is formed in the casing of valve 16. A spring is placed in opening 59 and urges a ball member 60 within one of the grooves 52 in piston 51.

Valve 20 includes a chamber 62 in which is placed a bellows 63. Bellows 63 is subjected on one side to fluid pressure substantially equivalent to suction pressure through inlet 64. On its opposite side, bellows 62 is placed under a predetermined force asserted by spring 64'; such side of the bellows is also subject to atmosphere pressure.

A port 65 is provided in valve 20 adapted to be closed by a valve member 66, such as a needle. Push rods 67 convey movement of bellows 63 to member 66. Oil is admitted to the valve, entering through inlet 68 from line 21 connecting valve 20 with chamber 56 of valve 16. When port 65 is opened by movement of needle 66, oil is free to flow through the port and through outlet 69 and line 26 to the crank case of the compressor. An auxiliary spring 70 operates in opposition to the adjustment spring to eliminate lost motion in the mechanism and to permit operation in a vacuum range of suction pressures.

Fluid pressure is provided to one side of bellows 63 through line 22 connecting control valve 20 with surge chamber 23. As shown in Figure l, a filter 71 is provided in the sump 8 of crank case. Pressure in the crank case substantially corresponds to suction pressure since the suction manifold is connected to the crank case. Pressure in crank case 7 forces oil from sump 8 through lines 25 and capillary tube 24 to surge chamber 23. Thus, as pressure in crank case 7 varies in accordance with changes in load as denoted by change in suction pressure, the liquid pressure imposed upon bellows 63 is retarded due to the surge chamber 23 and capillary tube 24.

It will be appreciated that the surge chamber is trapped so that refrigerant gas is always present therein. The capillary tube 24 retards the flow of oil into and from the surge chamber 23. The pressure in the surge chamber is a function of oil level (x). As level rises pressure increases and as level falls pressure decreases which results in the pressure imposed in one side of bellows 63 lagging behind the pressure change in crank case 8 and therefore lagging behind the change in suction pressure due to load change.

In normal operation, oil from pump 15 passes through line 17 to the inlet connection of valve 16. Dependent upon the position of piston 51 in chamber 59, certain of the outlets 8 are supplied with oil at full pressure, such oil being conducted by lines 19 to the power elements 14. Oil in chamber 50 passes through opening 57 into chamber 56. Chamber 56 is connected by means of line 21 to control valve 20. After valve port 65 in valve 20 is open, oil is free to pass through port 67 into the crank case, through outlet 69 and line 26.

Assuming port 65 of valve 20 is open, its efiective area is approximately three times as great as the area of opening 57 in valve 16. When port 65 is open, the

' oil pressure in chamber 56 is reduced to approximately 10% of full oil pressure. When valve member 66 moves to restrict port 65 in response to change in load conditions reflected by a change in liquid pressure substantially equivalent to suction pressure, oil pressure in chamber 56 increases. When port 65 is closed completely, oil pressure in chamber 56 increases to the full supply pres sure from the lubrication system. As the control oil pres sure in chamber 56 varies in response to the movement of needle 66 in valve 2%), piston 51 moves abruptly to open or to close outlets 58 in sequence. The application or removal ofoil pressure to or from the various power elements 14 operates the unloading mechanism 12 to unload or to load the various compressor cylinders.

As pointed out above, movement of needle 66 depends upon the pressure imposed upon bellows 63, such pressure being the oil pressure imposed through-surge chamber 23 as pressure in crank case 7 varies depending upon change in load. Such change in pressure is not reflected immediately in chamber 23 due to capillary tube 24. Assuming the pressure increases, then it is necessary that the refrigerant gas cotnained in surge chamber 23 be compressed to a greater degree before such change in load is reflected by movement of needle 66, thereby delaying or retarding the transmission of the pressure change to the control valve 20. Likewise, if the pressure in crank case 7 decreases due to decrease in load, pressure in surge chamber 23 is such that it need be reduced to permit the control valve to reflect this decrease in load thereby again imposing a time delay in response of valve 2%.

It will be appreciated chamber 23 is placed within the compressor housing in order that it may be maintained at approximately the same temperature as the crankcase to assure refrigerant gas in the surge chamber at all times.

The manner in which capillary tube 24 is connected to sump 8 of crank case 7, provides some advantages since it assures that the pressure on the opposite side of the oil filter is slightly less than actual crank case pressure. This connection may be made, however, at any place in the crank case below the oil level.

While we have described a capillary tube employed in connection with the surge chamber, it Will be understood other types of restrictions or orifices may be used in place thereof.

The present invention provides a capacity control arrangement for a reciprocating compressor in which suflicient time delay in response of the control instrument is provided to prevent rapid recycling. The invention is simple and may be included at slight expense in the control arrangement. The time delay so provided is automatic in operation and does not require care by an operator. Since the refrigeration system-is always filled with refrigerant when oil is added to the compressor, refrigerant gas is always present in the surge chamber.

While we have described a preferred embodiment of our invention, it will be understood our invention is not limited thereto since it may be otherwise embodied within the scope of the following claims.

We claim:

1. In a system of capacity control for reciprocating compressors, the combination of an oil pressure actuated element for holding a compressor valve in inoperative position, oil pressure actuated means for permitting or discontinuing the passage of oil to said element, means responsive to load conditions for varying the oil pressure imposed on the pressure actuated means to permit or to discontinue the passage of oil to said element in accordance with load conditions and a control for retarding the response of said means to change in load conditions.

2. In a system of capacity control for reciprocating compressors, the combination of oil pressure actuated elements for holding compressor valves in inoperative position, oil pressure actuated means for permitting or discontinuing the passage of oil tosaid elements, means responsive to fluid pressure substantially equivalent to suction pressure for varying the oil pressure imposed on the pressure actuated means thereby permitting or discontinuing the passage of oil to said elements and a control for retarding the response of said means to change in liquid pressure.

3. A system of capacity control according to claim 1 in which the control comprises a trapped surge chamber and a capillary tube connected to the chamberand the crank case of the compressor below the oil level therein.

4. A system of capacity control according to claim 3 in which a pump is provided to supply lubricant to moving parts of the compressor, a line connects the pump to the sump of the compressor, the capillary tube being connected to said line.

5. In a system of capacity control for reciprocating compressors, the combination of an oil pressure actuated element for holding a compressor valve in inoperative position, oil pressure actuated means for permitting or discontinuing the passage of oil to said element, means responsive to load conditions for varying the oil pressure imposed on the pressure actuated means to permit or to discontinue the passage of oil to saidelement in accordance with load conditions, a chamber containing refrigerant gas, a capillary tube connecting the chamber with a source of oil pressure which varies in accordance with changes in load, and a line connecting the surge chamber with said load responsive means to actuate the same, said surge chamber retarding the response of said load responsive means to change in load conditions.

6. In a system of capacity control for reciprocating compressors, the combination of oil pressure actuated elements for holdingcompressor valves in inoperative position, an oil pressure actuated valve permitting or discontinuing the passage of oil to said elements, a second valve responsive to load conditions for varying the oil pressure imposed on the first valve to permit or to discontinue the supply of oil in sequence to said elements, and a control for retarding the response of said second valve to change in load conditions.

7. A system of capacity control according to claim 6 in which said control comprises a trapped surge chamber and a capillary tube connected to the chamber and the crank case of the compressor below the oil level therein.

8. A system of capacity control according to claim 7 in which a pump is provided to supply lubricant to moving parts of the compressor, a line connects the pump to the sump of the compressor, the capillary tube connecting the surge chamber to said line.

9. In a system of capacity control for reciprocating compressors, the combination of oil pressure actuated elements for holding compressor valves in inoperative position, an oil pressure actuated valve permitting or discontinuing the passage of oil to said elements, a second valve for varying the oil pressure imposed on the first valve, said first valve including a chamber having a plurality of outlets connected with said elements, a piston movable in said chamber, means for imposing a predetermined pressure on said piston to move it longitudinally in one'direction in said chamber, a second chamber having an opening connecting it with the first chamber, oil flowing through said opening into the second chamber, said second chamber being connected to the second valve, said second valve having a port therein closed by a valve member, means for moving said valve member toward or from said port in response to oil pressure substantially equivalent to suction pressure, a control for retarding the response of said means, said control including a trapped surge chamber and a capillary tube connected to the crank case of the compressor below the oil level therein, said first valve including means for yieldably resisting longitudinal movement of said piston in said chamber, movement of said piston in said first chamber opening or closing the outlets therein to permit or to prevent passage of oil to the elements, oil pressure building up in said second chamber when passage of oil in said second valve is prevented thereby urging intermittent movement of the piston in an opposite direction against the resistance of the holding means to close the outlets to the elements in sequence in accordance with load conditions.

10. In combination with a compressor having a plurality of cylinders, a capacity control applied to at least some of the cylinders, said control including means adapted to hold the suction valves of the cylinders in inoperative position, power elements for actuating said means, said power elements being actuated by oil pressure, a pump for supplying oil to the compressor, a valve actuated by oil pressure serving to govern the supply of oil to said power elements, a second valve responsive to load conditions for varying the oil pressure imposed on the first valve and a control for retarding the response of said second valve to change in load conditions.

11. A capacity control according to claim 10 in which the retarding control comprises a trapped surge chamber and a capillary tube connected to the crank case of the compressor below the oil level therein.

12. A capacity control according to claim 11 in which a line is provided connecting the pump with the sump of the compressor, said capillary tube being connected to said line.

13. A capacity control according to claim 10 in which the retarding control includes a surge chamber containing refrigerant gas, a capillary tube connecting the surge chamber with the sump to provide a source of liquid pressure substantially equivalent to suction pressure, and a line connecting the surge chamber with said second valve toimpose said liquid pressure substantially equivalent to suction pressure on said valve to actuate the valve member thereof in accordance with changes in load.

References Cited in the file of this patent UNITED STATES PATENTS 865,388 Hill Sept. 10, 1907 1,096,265 Richards May 12, 1914 1,775,613 Ferris Sept. 9, 1930 2,009,608 Douglas July 30, 1935 2,065,204 Aikman Dec. 22, 1936 2,080,810 Douglas May 18, 1937 2,208,428 Nicolet July 16, 1940 2,267,448 Dooley .Dec. 23, 1941 2,274,337 Ritter Feb. 24, 1942 2,274,338 Cody Feb. 24, 1942 2,350,537 Scott June 6, 1944 2,387,117 Buehler Oct. 16, 1945 2,412,503 Gerteis Dec. 10, 1946 2,522,762 Neeson Sept. 19, 1950 2,626,099 Ashley Jan. 20, 1953 2,638,265 Newton May 12, 1953 

